1. Field of the Invention
The present invention is concerned with a new procedure for the flaring or belling of thick-walled tubes of flexible plastic material, and with a device for carrying out the procedure.
More specifically, the invention is applied to tubes of flexible plastic material, such as those made of polyethylene, having a relatively great thickness (difference between the internal and external diameters of the tubes) of about 4 mm or more.
2. Description of the Prior Art
Traditionally, the flaring of such tubes of relatively great thickness is accomplished by using mandrels, with heat, in such a way as to soften the wall of the tube enough to obtain the selected flaring.
Actually, such flaring is not durable for tubes of a high degree of thickness since the heat applied to the wall of the tube does not reach the central area of the wall unless the heat is applied for a long time, at a high heating temperature, which inevitably leads to a superficial fusion of the wall. Such a fusion is not recommended, since then there is deterioration of the tube.
The major disadvantage of the traditional procedure is the fact that the central area of the tube's wall is not heated which leads to a contraction of the flaring after the tube is cooled. Stated another way, the flaring tends to disappear, and the tube has a tendency to resume its initial diameter.